1. Field of the Invention
The present invention relates to a TFT-LCD (Thin-Film Transistor Liquid Crystal Display) slim bezel arrangement, and in particular to a fan-out wiring arrangement of TFT-LCD slim bezel arrangement.
2. The Related Arts
TFT-LCD stands for abbreviation of thin-film transistor LCD, which is one of active matrix liquid crystal displays (AM LCDs). Liquid crystal flat panel displays, especially TFT-LCD, is the only display device that is currently known display device that totally matches or is even superior to CRT (Cathode Ray Tube) display devices in general performances in respect of brightness, contrast, power consumption, lifespan, volume, and weight. The TFT-LCD has excellent performance, is extremely good for mass production, can be highly automatized, has a low cost for material, and shows potential prosperous future development and thus can quickly take the position of main stream product in the coming ear and will be the highlight of global economic growth of the 21st century.
A liquid crystal display panel is composed of an active area and a peripheral circuit area. The active area comprises a plurality of pixels arranged therein to form a pixel array. The peripheral circuit area comprises peripheral circuits arranged therein. Each pixel comprises a thin-film transistor (TFT) and a pixel electrode connected to the TFT and each pixel is surrounded by two adjacent scan lines and two adjacent data lines. It is often that the scan lines and the data lines extend from the active area to the peripheral circuit area and are electrically connected through the peripheral circuits to a driver IC (Integrated Circuit). Generally, the driver IC is of a specific size and the peripheral circuits are arranged to converge from the ends connected to the scan lines and the data lines to the site where the driver IC is located to form fan-out wirings.
In an upgraded development and for the market demand of TFT-LCD, a slim bezel arrangement is adopted to achieve aesthetics of visual perception. The arrangement of slim bezel requires a narrowed effective AA (Active Area)-TFT distance. However, the conventional fan-out wiring arrangement adopted in a single metal layer introduces a number of difficult in the design thereof:
(1) First of all, the slim bezel arrangement requires a severer fan-out height and the sum of lead-in fan-out line width and space must be equal to or less than 9 μm.
(2) The resolution of photolithography machine has a limit. That of Nikon photolithography machine is 2.5 μm and that of Cannon photolithography machine is 3.0 μm. Thus, for Nikon photolithography machine, the smallest lead-in space must be 2.5 μm.
(3) A large-sized TFT-LCD requires a thicker metal film. The critical dimension loss of wet etching is controlled at 2.5±1.0 μm. Consequently, the minimum AEI (After Etching Inspection) of product may achieve width/space (L/S) of the fan-out wiring that are 6.0 μpm/2.0 μm (for assessment made on Nikon machine, mask L/S=5.5 μm/2.5 μm).
(4) Referring to FIG. 1, a schematic view is given to illustrate the critical dimension of metal wire of prior art in wet etching. The first metal layer 11 is aluminum, which has a thickness of 3300 Å. The second metal layer is molybdenum, which has a thickness of 600 Å. The conventional arrangement of metal wiring is a two layer overlapping wiring arrangement. Since the metal wiring is formed through wet etching, it also needs to control tape angle in order to the lower corner angle to range from 20° to 60° . Under the assumption that metal sheet resistance (RS)=0.085, thickness=(Al) 3000 Å+(Mo) 600 Å=0.39 μm, calculation results show that to ensure Mo on the upper side will not get lost, the critical dimension (CD)>2×0.39 μm×ctg20° >2.2 μm.
Referring to FIG. 2, a schematic view is given to illustrate a conventional design of mask for single layer metal fan-out wiring. A mask 20 that has been subjected to photo-etching is placed on the metal layer so that a wet etching operation may be performed with the mask 20. To achieve the 7 μm design that is equal to fan-out wiring width plus spacing distance, the mask 20 must be arranged in such a way that the line width (L) is 4.5 μm and the spacing distance (S) is 2.5 μm, namely US=4.5 μm/2.5 μm. The known process and photolithography machine are not capable of achieving such as mask 20.
(5) Thus, the known manufacturing conditions cannot realize line width+spacing equal to or less than 8 μm. A trial test can only be carried out with Line/Space=6.5 μm/2.5 μm, the minimum line CD may be 3.0 μm and it is of extremely high risk to be broken by air knife (AK). Further, if the array side fan-out wire is broken, due to the metal wires are arranged extremely densely, it is not possible to repair, making the product yield rate low.